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Afire retardant is a substance that is used to slow down or stop the spread of fire or reduce its intensity. This is commonly accomplished by chemical reactions that reduce theflammability of fuels or delay theircombustion.[1][2] Fire retardants may also cool the fuel through physical action orendothermic chemical reactions. Fire retardants are available as powder, to be mixed with water, asfire-fighting foams andfire-retardant gels.
Fire retardants are commonly used infire fighting, where they may be appliedaerially or from the ground.
In general, fire retardants reduce the flammability of materials by either blocking the fire physically or by initiating achemical reaction that stops the fire.
There are several ways in which thecombustion process can be retarded by physical action:
Commonly used fire retardant additives include mixtures ofhuntite (Mg3Ca(CO3)4) andhydromagnesite (Mg5(CO3)4(OH)2·4H2O),aluminium hydroxide (Al(OH)3), andmagnesium hydroxide (Mg(OH)2). When heated,aluminium hydroxide dehydrates to formaluminum oxide (alumina,Al2O3, releasing water vapor in the process. This reactionabsorbs a great deal ofheat, cooling the material into which it is incorporated. Additionally, alumina residue forms a protective layer on the material's surface. Mixtures ofhuntite andhydromagnesite work in a similar manner. They endothermically decompose releasing both water and carbon dioxide,[3][4] giving fire retardant properties[5][6][7] to the materials in which they are incorporated.
Class A foam is used as a fire retardant in 2.5 gallon [APW] and [CAFS] extinguishers to contain incipient brush fires and grass fires by creating a fire break. Other chemical retardants are capable of rendering class A material and Class B fuels non-flammable and extinguishing class A, class B, and some class D fires.[citation needed] Fire retardant slurries dropped from aircraft are normally applied ahead of awildfire to prevent ignition, while fire suppression agents are used to extinguish fires.
Objects may be coated with fire retardants. For example, Christmas trees are sprayed with retardants, as a tree dries out it becomes very flammable and a fire-hazard.
Steel structures have a fire retardant coating around columns and beams to prevent structural elements from weakening during a fire.
Dormitories in the US are considering or are required by law to use these products.Intumescent coatings are used by various dormitories and in school buildings, especially those with historic structures that lackfire sprinkler systems.[10]
Early fire retardants were mixtures of water and thickening agents, and later includedborates[11] and ammonium phosphates.[citation needed]
Generally, fire retardants are dropped from aircraft or applied by ground crews around awildfire's edges in an effort to contain its spread. This allows ground crews time to work to extinguish the fire. However, when needed, retardant can also be dropped directly onto flames to cool the fire and reduce flame length.[12]
Aerial firefighting is a method to combat wildfires using aircraft. The types of aircraft used include fixed-wing aircraft and helicopters. Smokejumpers and rappellers are also classified as aerial firefighters, being delivered by parachute from a variety of fixed-wing aircraft, or rappelling from helicopters. Chemicals used to fight fires may include water, water enhancers, or specially-formulated fire retardants.[13]
Fire retardants applied towildfires are usually a mixture of water and chemicals designed to wet the area as well as chemically retard a fire's progression through vegetation. Typically they are colored[14] so that the application area can be seen from the air.Fire retardant gel based retardants which meetNFPA Standard 1150 are also used. These are dyed other colors to differentiate them from the traditional red retardant. The gels and their dyes are designed to biodegrade naturally.[15]
Any fire retardant approved for use against wildfires on US Federal lands must be included on theUnited States Forest Service Qualified Products List.[16] To be added to that list, the product must be tested by Wildland Fire Chemical Systems, a division of the National Technology and Development Program. This process can take up to two years.[17]Phos-Chek is a brand of long-term retardant currently approved for wildland fire use.[18]
Researchers at theUniversity of Southern California's Department of Civil and Environmental Engineering published a report titled "Metals in Wildfire Suppressants".[19] The report provided the first-ever chemical analysis of Phos-Chek fire retardant, which the research team studied because it is the most widely used. The USC researchers found that Phos-Chek contains high levels ofheavy metals: 14.4 mg/L ofcadmium, 72.7 mg/L ofchromium, and 119 mg/L ofvanadium. These numbers exceed California toxic waste limits by 14 times, 14 times, and 5 times, respectively.
Phos-Chek also has a consumer-based fire retardant spray called Wildfire Home Defense that is effective immediately after application and that remains effective until it is washed off with heavy water levels. It is designed to be applied to fuel beds around homes and outbuildings to create a firebreak in the fuels leading up to each structure.[20] Ember Bloc is another consumer-based fire retardant gel that can be applied to the exterior of one's house and nearby structures to help protect against both embers and flames in a wildfire. It has a unique ability to cling onto the side of a house to withstand high heat and windy conditions.[21]
Forest fire retardants that are used are generally considerednon-toxic,[22] but even less-toxic compounds carry some risk when organisms are exposed to large amounts.[23]As of 2008, drops within 300 feet of bodies of water are generally discouraged unless lives or property are directly threatened.[24] TheUS Forest Service is the governing agency that conducts research and monitors the effect of fire retardants on wildland systems in the US.[25][26]
Some specialized indoor fire retardants are organichalides (haloalkanes) such asHalon andPhostrEx, which are proven to be toxic.
Studies have also shown that a drop of the retardant chemical directly into a stream may cause a sufficientammonia concentration in the water, which islethal to fish and otheraquatic organisms.[27]
Another notable health concern is that fire-suppressant foams are especially toxic to fish in standardized soft andhard water, possibly due to surfactants.[28]
